1. Field of the Invention
The present invention relates to an inkjet print head.
2. Description of Related Art
An on-demand piezoelectric type inkjet print head well known in the art, includes: a cavity unit having a plurality of nozzles and a plurality of pressure chambers, each corresponding to one nozzle; and a plate-shaped piezoelectric actuator formed of stacked piezoelectric sheets (green sheets manufactured of a ceramic material) alternately having individual electrodes formed for each pressure chamber and common electrodes common to a plurality of neighboring pressure chambers. This piezoelectric actuator has to be superimposed on the cavity unit so that each individual electrode in the actuator will correspond to an individual pressure chamber.
In order to assemble the piezoelectric actuator with the cavity unit, which is made of metal materials and the like, marks are previously formed on the peripheral surface of the stacked green sheets, before the green sheet stack is sintered. After sintering, a resultant piezoelectric actuator is located on the cavity unit by aligning the marks on the peripheral surface of the piezoelectric actuator with prescribed positions on the cavity unit.
It is noted, however, that the step for sintering the green sheet causes the green sheet to shrink, thereby decreasing the pitch between individual electrodes formed on the piezoelectric sheets. For this reason, shrinkage is taken into account when manufacturing green sheets used to produce the piezoelectric sheets. Despite this, the amount of shrinkage is different in the center and peripheral portions of the sheets. Further, the amount of shrinkage is different according to the position in the sintering furnace. Accordingly, when assembling the piezoelectric actuator with the cavity unit, even by aligning the preformed marks on the piezoelectric actuator with the prescribed positions on the cavity unit, the individual electrodes will not be in line with the pressure chambers in the cavity unit.
In order to solve this problem, it is conceivable to provide a print head as shown in FIG. 1.
The conceivable print head includes: a cavity unit 54 and a plate-shaped piezoelectric actuator 56. The cavity unit 54 has a plurality of pressure chambers 55 and a plurality of nozzles (not shown), each of which is in fluid communication with a corresponding pressure chamber 55. The plate-shaped piezoelectric actuator 56 is formed of piezoelectric sheets (green sheets manufactured of a ceramic material) 50 stacked alternately with individual electrodes 51 (FIG. 2) and common electrodes (not shown).
FIG. 2 shows one of several piezoelectric sheets 50, on which the individual electrodes 51 are provided. As shown in FIG. 2, a plurality of individual electrodes 51 are arranged in rows along the long sides of the piezoelectric sheet 50. One centrally-located individual electrode 51 on each side of the piezoelectric sheet 50 is replaced by an elongated electrode 52 having an extended part 52a that extends to the outer edge of the piezoelectric sheet 50. The extended part 52a is used to determine the position of the individual electrodes 51 externally.
As shown in FIG. 1, positioning marks 54a are provided on the cavity unit 54. When assembling the piezoelectric actuator 56 and the cavity unit 54, the extended parts 52a are aligned with the positioning marks 54a in order to align each individual electrode 51 accurately with one pressure chamber 55.
It is, however, difficult to accurately discern the extended parts 52a of the electrodes 52 exposed on the side surfaces of the piezoelectric actuator 56, due to the extremely thin shape of the electrodes 52.
In view of the above-described drawbacks, it is an objective of the present invention to provide an improved inkjet print head, which is capable of facilitating an accurate alignment of individual electrodes in the piezoelectric actuator to pressure chambers in the cavity unit when assembling the piezoelectric actuator and cavity unit. It is another object to provide an improved method of producing an inkjet print head.
In order to attain the above and other objects, the present invention provides an inkjet print head comprising: a cavity unit having a plurality of nozzles and a plurality of pressure chambers which are provided in one-to-one correspondence with the plurality of nozzles; and a piezoelectric actuator provided over the cavity unit, the piezoelectric actuator including: a plurality of piezoelectric sheets which are stacked one on another, each piezoelectric sheet being elongated over the plurality of pressure chambers; a plurality of individual electrodes provided on each of several ones of the plurality of piezoelectric sheets; and at least one detecting portion, formed on each of the several piezoelectric sheets, for being used to detect the position of the individual electrodes by being irradiated with light along the stacked direction of the piezoelectric sheets, the piezoelectric actuator and the cavity unit being positioned relative to each other using the at least one detecting portion on each of the several piezoelectric sheets, thereby allowing each individual electrode to be located substantially at a position corresponding to one pressure chamber.
According to another aspect, the present invention provides an inkjet print head comprising: a cavity unit having a plurality of nozzles and a plurality of pressure chambers which are provided in one-to-one correspondence with the plurality of nozzles; and a piezoelectric actuator provided over the cavity unit, the piezoelectric actuator including: a plurality of piezoelectric sheets which are stacked one on another, each piezoelectric sheet being elongated over the plurality of pressure chambers; a plurality of individual electrodes provided between at least two adjacent ones of the plurality of piezoelectric sheets; and at least one detecting portion, formed on at least one of the plurality of piezoelectric sheets, for being used to detect the position of the individual electrodes by being irradiated with light along the stacked direction of the piezoelectric sheets, the piezoelectric actuator and the cavity unit being positioned relative to each other using the at least one detecting portion, thereby allowing each individual electrode being located substantially at a position corresponding to one pressure chamber.
According to a further aspect, the present invention provides an inkjet print head, comprising: a cavity unit which is elongated in a lengthwise direction, the cavity unit having a plurality of pressure chambers arranged in one row, the cavity unit being provided with two cavity-unit detecting portions, which are arranged along the lengthwise direction and which are located on both ends of the elongated cavity unit in the lengthwise direction; and a piezoelectric actuator provided over the cavity unit, the piezoelectric actuator including: a plurality of piezoelectric sheets, a plurality of groups of individual electrodes, and a plurality of common electrodes, which are alternately stacked on one another, each piezoelectric sheet being elongated over the plurality of pressure chambers, each common electrode being elongated over the plurality of pressure chambers, each group of individual electrodes including a plurality of individual electrodes which are arranged in one row in one to one correspondence with the plurality of pressure chambers; and two detecting portions, formed on at least one of the plurality of piezoelectric sheets at two positions that are located on both ends of the row of the individual electrodes and that are shifted from the common electrodes, for being used to detect the position of the individual electrodes by being irradiated with light along the stacked direction, the piezoelectric actuator and the cavity unit being positioned relative to each other with an average position of the two detecting portions being substantially coincident with an average position of the two cavity-unit detecting portions, thereby allowing each individual electrode being located substantially at a position corresponding to one pressure chamber.
According to another aspect, the present invention provides a method of producing an inkjet print head, the method comprising the steps of: preparing a cavity unit, which is provided with a plurality of pressure chambers and which is formed with at least one cavity-unit detecting portion; preparing a plurality of green sheets, for a plurality of piezoelectric sheets, from piezoelectric material that transmits light therethrough upon irradiation with the light; printing a plurality of individual electrodes and at least one detecting portion on each of several ones of the plurality of piezoelectric green sheets and printing a common electrode on each of the other remaining piezoelectric green sheets at a position that is shifted from the position where the at least one detecting portion is printed on the several piezoelectric green sheets, the at least one detecting portion and the individual electrodes being made of the same material that blocks light when irradiated with light; stacking the plurality of piezoelectric green sheets one on another; sintering the stacked piezoelectric green sheets to form a piezoelectric actuator; radiating light onto the piezoelectric actuator in the stacked direction, thereby causing each detecting portion to form a shadow, picking up at least one image of the at least one shadow, to obtain information on the position of the at least one detecting portion; picking up an image of the at least one cavity-unit detecting portion on the cavity unit, to obtain information on the position of the at least one cavity-unit detecting portion; positioning the piezoelectric actuator and the cavity unit relative to each other based on the information on the position of the at least one detecting portion and on the position of the at least one cavity-unit detecting portion, thereby allowing each individual electrode to be positioned in correspondence with a corresponding pressure chamber; and bonding the piezoelectric actuator and the cavity unit relative to each other.